The median age of the world's population is increasing because of a
decline in fertility and a 20-year increase in the average life span during
the second half of the 20th century.1 These
factors, combined with elevated fertility in many countries during the 2 decades
after World War II (i.e., the "Baby Boom"), will result in increased numbers
of persons aged ≥65 years during 2010-2030.2 Worldwide,
the average life span is expected to extend another 10 years by 2050.1 The growing number of older adults increases demands
on the public health system and on medical and social services. Chronic diseases,
which affect older adults disproportionately, contribute to disability, diminish
quality of life, and increased health- and long-term–care costs. Increased
life expectancy reflects, in part, the success of public health interventions,2 but public health programs must now respond to
the challenges created by this achievement, including the growing burden of
chronic illnesses, injuries, and disabilities and increasing concerns about
future caregiving and health-care costs. This report presents data from the
U.S. Bureau of the Census, the World Health Organization, and the United Nations
on U.S. and global trends in aging, including demographic and epidemiologic
transitions, increasing medical and social costs related to aging, and the
implications for public health.

U.S. Trends

In the United States, the proportion of the population aged ≥65 years
is projected to increase from 12.4% in 2000 to 19.6% in 2030.3 The
number of persons aged ≥65 years is expected to increase from approximately
35 million in 2000 to an estimated 71 million in 2030,3 and
the number of persons aged ≥80 years is expected to increase from 9.3 million
in 2000 to 19.5 million in 2030.3 In 1995,
the most populous states had the largest number of older persons; nine states
(California, Florida, Illinois, Michigan, New Jersey, New York, Ohio, Pennsylvania,
and Texas) each had more than one million persons aged ≥65 years.4 In 1995, four states had ≥15% of their population
aged ≥65 years; Florida had the largest proportion (19%).5 By
2025, the proportion of Florida's population aged ≥65 years is projected
to be 26%5 and ≥15% in 48 states (all
but Alaska and California).5

The sex distribution of older U.S. residents is expected to change only
moderately. Women represented 59% of persons aged ≥65 years in 2000 compared
with an estimated 56% in 2030.3 However,
larger changes in the racial/ethnic composition of persons aged ≥65 years
are expected. From 2000 to 2030, the proportion of persons aged ≥65 years
who are members of racial minority groups (i.e., black, American Indian/Alaska
Native, Asian/Pacific Islander) is expected to increase from 11.3% to 16.5%4; the proportion of Hispanics is expected to increase
from 5.6% to 10.9%.4

Global Trends

In 2000, the worldwide population of persons aged ≥65 years was an
estimated 420 million, a 9.5 million increase from 1999.2 During
2000-2030, the worldwide population aged ≥65 years is projected to increase
by approximately 550 million to 973 million,3 increasing
from 6.9% to 12.0% worldwide, from 15.5% to 24.3% in Europe, from 12.6% to
20.3% in North America, from 6.0% to 12.0% in Asia, and from 5.5% to 11.6%
in Latin America and the Caribbean.2 In
Sub-Saharan Africa, an area where both fertility and mortality rates are high,
the proportion of persons aged ≥65 years is expected to remain small, increasing
from an estimated 2.9% in 2000 to 3.7% in 2030.2 The
largest increases in absolute numbers of older persons will occur in developing
countries.* During 2000-2030, the number of persons in developing countries
aged ≥65 years is projected to almost triple, from approximately 249 million
in 2000 to an estimated 690 million in 2030,3 and
the developing countries' share of the world's population aged ≥65 years
is projected to increase from 59% to 71%.2 However,
migration patterns could influence these projections.

The aging of the world's population is the result of two factors: declines
in fertility and increases in life expectancy.2 Fertility
rates declined in developing countries during the preceding 30 years and in
developed countries throughout the 20th century.2 In
addition, in developed countries, the largest gain ever in life expectancy
at birth occurred during the 20th century, averaging 71% for females and 66%
for males.2 Life expectancy at birth in
developed countries now ranges from 76 to 80 years.2 Life
expectancy also has increased in developing countries since 1950, although
the amount of increase varied. A higher life expectancy at birth for females
compared with males is almost universal. The average sex differential in 2000
was approximately 7 years in Europe and North America but less in developing
countries.2

Demographic Transition

The world has experienced a gradual demographic transition from patterns
of high fertility and high mortality rates to low fertility and delayed mortality.2 The transition begins with declining infant and
childhood mortality, in part because of effective public health measures.2 Lower childhood mortality contributes initially
to a longer life expectancy and a younger population. Declines in fertility
rates generally follow, and improvements in adult health lead to an older
population. As a result of demographic transitions, the shape of the global
age distribution is changing. By 1990, the age distribution in developed countries
represented similar proportions of younger and older persons.2 For
developing countries, age distribution is projected to have similar proportions
by 2030.2

Epidemiologic Transition

The world also has experienced an epidemiologic transition in the leading
causes of death, from infectious disease and acute illness to chronic disease
and degenerative illness. Developed countries in North America, Europe, and
the Western Pacific already have undergone this epidemiologic transition,
and other countries are at different stages of progression. In 2001, the leading
causes of death in developed countries, which had low child and delayed adult
mortality, were primarily cardiovascular diseases and cancer, followed by
respiratory diseases and injuries.6 The
leading causes of death in African countries, which had high child and adult
mortality, were infectious and parasitic diseases (e.g., human immunodeficiency
virus/acquired immunodeficiency syndrome, malaria, childhood diseases, and
diarrheal disease), respiratory infections, perinatal conditions, cardiovascular
diseases, cancer, and injuries.6

The epidemiologic transition, combined with the increasing number of
older persons, represents a challenge for public health. In the United States,
approximately 80% of all persons aged ≥65 years have at least one chronic
condition, and 50% have at least two.7 Diabetes,
which causes excess morbidity and increased health-care costs, affects approximately
one in five (18.7%) persons aged ≥65 years, and as the population ages,
the impact of diabetes will intensify.7 The
largest increases in diabetes are expected among adults aged ≥75 years,
from 1.2 million women and 0.8 million men in 2000 to 4.4 million women and
4.2 million men in 2050.8 As U.S. adults
live longer, the prevalence of Alzheimer's disease, which doubles every 5
years after age 65, also is expected to increase.7 Approximately
10% of adults aged ≥65 years and 47% of adults aged ≥85 years suffer
from this degenerative and debilitating disease.7

Chronic conditions also can lead to severe disability. For example,
in the United States, arthritis affects approximately 59% of persons aged
>65 years and is the leading cause of disability.9 However,
some studies have shown that disability can be postponed through healthier
lifestyles.10 Disability among older U.S.
adults, as measured by limitations in instrumental activities of daily living,
has declined since the early 1980s.11 Disability
also is measured by limitations in activities of daily living (ADL), a common
factor leading to the need for long-term care.11 Recent
studies using ADL measures have shown varied trends in disability.11

Impact on Medical and Social Services

The increased number of persons aged ≥65 years will potentially lead
to increased health-care costs. The health-care cost per capita for persons
aged ≥65 years in the United States and other developed countries is three
to five times greater than the cost for persons aged <65 years, and the
rapid growth in the number of older persons, coupled with continued advances
in medical technology, is expected to create upward pressure on health- and
long-term–care spending.12 In 1997,
the United States had the highest health-care spending per person aged ≥65
years ($12,100), but other developed countries also spent substantial amounts
per person aged ≥65 years, ranging from approximately $3,600 in the United
Kingdom to approximately $6,800 in Canada.13 However,
the extent of spending increases will depend on other factors in addition
to aging.12

The demands associated with long-term care might pose the greatest challenge
for both personal/family resources and public resources. In the United States,
nursing home and home health-care expenditures doubled during 1990-2001, reaching
approximately $132 billion14; of this, public
programs (i.e., Medicaid and Medicare) paid 57%, and patients or their families
paid 25%.14 In addition, during 2000-2020,
public financing of long-term care is projected to increase 20%-21% in the
United Kingdom and the United States and 102% in Japan.15 However,
these increases will be less if public health interventions decrease disability
among older persons, helping them to live independently.

The projected growth in the elderly support ratio (i.e., the number
of persons aged ≥65 years per 100 persons aged 20-64 years) also is a concern.2 If the number of working taxpayers relative to
the number of older persons declines, inadequate public resources and fewer
adults will be available to provide informal care to older, less able family
members and friends. However, the ratio does not account for potential increases
in the numbers of persons aged ≥65 years who continue to work and/or care
for themselves.

The anticipated increase in the number of older persons will have dramatic
consequences for public health, the health-care financing and delivery systems,
informal caregiving, and pension systems. Although more attention has been
given to population aging projections and their implications in developed
countries, greater numbers of older adults and increasing chronic disease
will place further strain on resources in countries where basic public health
concerns (e.g., control of infectious diseases and maternal and child health)
are yet to be addressed fully.

To address the challenges posed by an aging population, public health
agencies and community organizations worldwide should continue expanding their
traditional scope from infectious diseases and maternal/child health to include
health promotion in older adults, prevention of disability, maintenance of
capacity in those with frailties and disabilities, and enhancement of quality
of life. Because behaviors that place persons at risk for disease often originate
early in life, the public health system should support healthy behaviors throughout
a person's lifetime.16 Public health also
should develop and support better methods and systems to monitor additional
health outcomes that are related to older adults, such as functioning and
quality of life.

CDC's Advisory Committee to the Director has identified five roles for
CDC to promote health and prevent disease in older adults: (1) to provide
high-quality health information and resources to public health professionals,
consumers, health-care providers, and aging experts; (2) to support health-care
providers and health-care organizations in prevention efforts; (3) to integrate
public health prevention expertise with the aging services network; (4) to
identify and implement effective prevention efforts; and (5) to monitor changes
in the health of older adults. These roles will require new efforts to address
the special needs of older adults and to deliver programs in communities in
which older adults work, reside, and congregate. Existing public health programs
will be required to examine whether they meet the needs of an aging population.

*The "developing" and "developed" country categories used in this report
correspond directly to the "less developed" and "more developed" classification
employed by the United Nations. Developed countries comprise all nations in
Europe and North America, and Japan, Australia, and New Zealand. The remaining
nations are classified as developing countries. Although these categories
are used commonly for comparative purposes, they no longer accurately reflect
developmental differences among countries.2